<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    li{
      width: 400px;
      height: 50px;
      background-color: #e1e7d3;
      margin-top: 20px;
    }
  </style>
</head>
<body>
  <div id="app">
    <button @click="addArr">添加li</button>
    <ul>
      <li v-for="item in arr" :key="item">
        {{item}}
      </li>
    </ul>
  </div>
  <script src="./vue.global.js"></script>
  <script>
    const { createApp } = Vue;
    const  app = createApp({
      data(){
        return {
          arr: [1,2,3,4]
        }
      },
      methods: {
        addArr(){
          this.arr.push(this.arr.length+1);
          const oul = document.querySelector('ul');
          this.$nextTick(() => {
            console.log(oul.children, 22);
            oul.lastElementChild.style.background = 'red';
          })
          
          console.log(oul.children, 11);
         
        }
      },
    })

    app.mount('#app')
  </script>
</body>
</html>